1. Field of the Invention
The present invention relates to a control method, more particularly to a method for controlling a resonant converter.
2. Description of the Related Art
Shown in FIG. 1 is a conventional half-bridge LLC resonant converter 900 including first and second power switches Q1, Q2, and operable for generating an output voltage VO. When the LLC resonant converter 900 is connected to a load RL that is excessively large or is shorted-circuited, the LLC resonant converter 900 will output a large current that may damage electronic components. Furthermore, during the soft-start stage, the output voltage VO generated by the LLC resonant converter 900 has low linearity, which hinders the use of the LLC resonant converter 900 in some applications such as servers.
Shown in FIG. 2 is another conventional LLC resonant converter 900′ that employs a current-limiting circuit 910 for limiting voltage of a resonant capacitor Cr of the resonant converter 900′ so as to limit an output current of the resonant converter 900′. However, during actual operation, energy stored by the resonant capacitor Cr can still be transferred to the output side of the LLC resonant converter 900′ via the current-limiting circuit 910. As a result, the output current of the LLC resonant converter 900′ is not limited precisely. Moreover, use of the current-limiting circuit 910 does not improve linearity of an output voltage VO of the LLC resonant converter 900′ during the soft-start stage of the LLC resonant converter 900′.